1/2HP Craftsman Garage Door Opener

After almost about 14 years of problem free operation, our garage door opener Craftsman 139.53635 SRT, failed. When I tried to open or close, the light on it would blink 5 times, pause for a while, and repeat the same sequence again.

Whenever there is a problem like this, I try to repair it first. What I needed was the circuit diagram for the Craftsman 139.53635 SRT garage door opener, but nobody seemed to have it. The best I could find was the verbal description of the circuit, which I converted into a block diagram as shown below.

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The main controller IC is the 28 pin chip that works off of 60 Hz clock signal. The following inputs go into this chip: RPM sensor, UP/DOWN Limit (from UP/DOWN limit switches), UP/DOWN sensors (from adjustable resistors to adjust how far the door goes up/down), radio RCVR (from the radio receiver that takes the signals from the remote units).

There are three outputs from this IC. The light, the door up, and the door down. These signals drive NPN transistors, which in turn drive the three big relays on the circuit board to power the light, and the motor in two directions.

Three wires are connected to the motor, ground and the two hot wires to spin the motor in either direction. It was easy to check that the motor was good. I positioned the garage door somewhere in the middle and momentarily activated the hot wires to see that the motor was spinning.

Then I took the circuit board out and powered it on my work bench. I grounded the correct end of the relay coil to see that it was clicking, for each relay. If you look at the circuit, the only remaining parts that can possibly fail are the driving transistors.

These transistors were Surface Mount Devices (SMD), very very small. It is amazing that they lasted as long as they did. Unless you have tiny tiny fingers, they are also very hard to work with. I de-soldered all three transistors, but I could immediately see that even if I had brand new ones to replace them, I would not be able to solder them back in. In fact, when I sneezed once, I lost one of the transistors permanently.

I soldered three wire-wrapping wires (the type of wire shown in the pictures below), and soldered my three big-mama NPN power transistors to those wires. This idea worked well. I installed the circuit board back into its housing. And, yes, the garage door started working again. It worked without any problems for about 3 more months.

When I saw the exact same failure pattern after about 3 months, I did not want to spend any more time on this garage door opener, and made a trip to Sears to buy the same model number. The closest one was 1/2 HP Craftsman model 139.53920DM. I bought and installed the new garage door opener.

But nothing is easy in life. The new garage door opener came with only one remote unit and it was transmitting at a different frequency than my old garage door opener. Over the years I had collected a variety of remote units for my old garage door opener. They were all perfectly functional. Replacing every old remote with new ones would cost me more than the garage door itself. But the question remained. How could I use my old remotes with the new garage door opener?

The diagram below shows the solution to this puzzle.

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There are two parts to this solution. First, we take the 3V lithium ion battery out of the new garage door opener, and put a rubber band around the transmit button so it is permanently pushed down. If we give 3 Volts into the battery terminals, the new remote unit will send a signal to activate the garage door. The signal goes out only when the power is applied, not when it is removed.

Second, we use the radio receiver from the old garage door opener. To do this we get rid of everything from the old garage door opener except the main circuit board. We put 2 inch spacers in all four corners and connect the front and the back covers together to protect the circuit board as shown in the pictures below.

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To figure out the radio receiver pin into the controller IC, I started from pin 1 and continued to test each pin in turn. While I measured the voltage (with respect to ground), I pressed the old garage door opener remote unit. When I found the right pin, whenever I pressed the remote unit, the voltage would go high for about two seconds, and then go low. The picture below shows the right pin to use.

Yellow wire is the ground.

Red wire (fifth pin from left) is radio receiver pin.

The high voltage is closer to 5 volts so I used 3 diodes (3 x 0.7 V) to reduce the voltage to about 3 volts. I am not sure if this was necessary, but I did not want to take a chance and destroy the new remote controller unit.

We have been using this configuration for months now without any problems. The only minor issue is that it takes a little longer to open or close the door since the signal has to go through two separate circuits. But the delay is not noticeable.

6 Responses to 1/2HP Craftsman Garage Door Opener

Excellently written and described. The only pointer I could add that works on any SMT component, is to first glue the component into place and use hemostat, needle nose pliers or tweezers to place it. Just a tiny drop of a super-type glue will do. I prefer to apply the glue with a toothpick, just to avoid applying too much. Make sure the legs of the component are lined up with the contacts on the board and apply the solder and heat.

Hi Paul-
Thank you for the pointers on how to work with surface mount (SMD) devices. I will try your trick next time around. Do you have any ideas on how to remove SMD device that has many pins on all four sides? By the time you heat up to desolder the next pin, the previous one will get cold and freeze up. Is there a special device that might remove those chips?
Thanks Paul

Hello “Nev.” I am in the beginning stages of diagnosing trouble with my Liftmaster model 1355 (1/2 HP) garage-door opener. Your block diagram and description are helpful. By the way, the external part number is 41A3625, the logic circuit board has a marking 14PC377B, and the circuit board’s part number (according to the instructions) is 41A5021-1H-315.